I researched road disc brake issues on the popular bike forums but found nothing on mountain descending with road bike discs. Mountain bike discs noise and vibration is covered with thousands of opinions and suggestions. Next I downloaded the manuals from the Shimano site and read through them.
I noticed that the BR-RS785 had 4 different pad options: resin or metal pads, with or without fins. I knew I had the fins but wasn’t sure if the pads that came stock in the Defy were fiber or metal. I called the Giant shop and talked to the mechanic and he wasn’t sure either. He said I should bring the bike up but between his uninspiring unfamiliarity with the brakes, a 2 hours round trip drive, and foreseeing a parking lot test ride leading to “no trouble found” I decided I needed to troubleshoot this myself. I’ve have had numerous disc brakes of my mountain bikes over the past 18 years so was familiar with pad removal and cleaning. I took out the pads and discovered they were the J02A Resin Pads w/Fin. Over the years I had gravitated towards metal pads on my XTR disc brakes so decided I should get some for the road bike. When I googled for the J04C Metal Pad with Fin, it was one of the rare times you couldn’t find something to buy off the web. A few e-tailers in Europe showed them but without stock and there were no US stores showing the item, let alone stock. It appeared the J04C pads were only available on eBay directly from Taiwan and no where else in the world. I wondered if I was the proverbial early adopter armed with “Beta” brake setup. In further research I discovered the J04C pad not only worked in my road bike but also was the new pad for my XTR brakes. I felt a little better that at least I had the same basic caliper and pad arrangement as the established mountain bike technology.
I reached out to Stephanie at the Giant shop explaining the scary undulations and excessive noise of the fiber pads on my first descent despite plenty of break in period and asked if she could help locate the metal pads. She called Shimano and was able to get a set of J04C pads shipped from Shimano so I could try them in the Defy. She apologized for my struggles and said she would comp them to me in exchange for further testing and feedback. Kudos to Stephanie @ Giant Denver.
Road Disc 